The language has changed in that respect - arrays and hashes only interpolate into double-quoted strings if they end in a postcircumfix, that is any bracketing characters coming after an expression.
say "array: @array"; # interpolates nothing
say "array: @array"; # interpolate all elements
say "array: @array"; # interpolate one element
say "array: @array.sort"; # no interpolation, does not
# end with something brackety
say "array: @array.sort()"; # interpolates sorted array
Rakudo implements those cases according to the specification.
See also: strings, arrays, hashes, S02: Literals (scroll down)
- links to (nearly) everything that is Perl 6.